1. Field of the Invention
The present invention generally relates to a disk array system, particularly to a copying technique of preparing a duplicate of a disk drive.
2. Description of the Related Art
In general, as a disk array (RAID: redundant arrays of inexpensive disks) system, a RAID (RAID-0) system including a striping constitution in which data is scattered by a block unit and having level 0, a RAID (RAID-1) system including a mirroring constitution in which the same data is stored in a plurality of disk drives and having level 1 and the like are well known.
A disk array controller (hereinafter referred to as a RAID controller) which realizes a RAID-1 function has a data restoring function called a rebuilding or reconstruction function. By the rebuilding function, data stored in a failed disk drive (HDD) can be restored in a disk drive for replacement.
All the data stored in the existing disk drive is copied into a new disk drive using the rebuilding function, and accordingly a copying function of preparing a duplicate disk drive can be realized. A prior technique has been proposed in which mirroring pairs constituted by a plurality of disk drives are rebuilt using the copying function (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 9-269871).
In the prior technique, when one of the disk drives constituting the mirroring pair having a high priority order fails, a mirroring pair having a low priority order is eliminated, and the disk drive constitutes a new mirroring pair with the disk drive having a high priority order.
In general, when a duplicate disk drive is prepared using the rebuilding function of the RAID controller, one disk drive is forced to fail from a state in which redundancy (optimal) is maintained (constitution of the RAID-1 system), and replaced with a disk drive for copying after a state of non-redundancy (degrade) to execute a duplicating operation (copying operation of all data).
However, in the usual method, the redundancy state is forcibly brought into a non-redundancy state in the constitution of the RAID-1 system. Therefore, when trouble occurs in the existing disk drive as an original of a duplicate, there is a possibility that the disk falls into a situation in which not only duplicate data but also original data cannot be restored.